Ablation electrode assembly and methods for improved control of temperature and minimization of coagulation and tissue damage

ABSTRACT

The present invention pertains to multiple piece irrigated ablation electrode assemblies wherein the irrigation channels are insulated or separated from at least one temperature sensing mechanism within the distal portion of the electrode assembly. The present invention further pertains to methods for improved assembly and accurate measurement and control of the electrode temperatures while effectively irrigating the device and target areas.

BACKGROUND OF THE INVENTION

a. Field of the Invention

The present invention pertains generally to ablation electrodeassemblies. More particularly, the present invention is directed towardablation electrode assemblies for use in the human body having at leastone temperature sensing device and a mechanism for irrigating theablation assembly and targeted areas. The present invention also relatesto methods for improved assembly and accurate measurement and control ofthe electrode temperatures while effectively irrigating the device andtarget areas.

b. Background Art

Electrophysiology catheters are used for an ever-growing number ofprocedures. For example, catheters are used for diagnostic, therapeutic,and ablative procedures, to name just a few examples. Typically, thecatheter is manipulated through the patient's vasculature and to theintended site, for example, a site within the patient's heart.

The catheter typically carries one or more electrodes, which may be usedfor ablation, diagnosis, or the like. There are a number of methods usedfor ablation of desired areas, including for example, radiofrequency(RF) ablation. RF ablation is accomplished by transmission ofradiofrequency energy to a desired target area through an electrodeassembly to ablate tissue at the target site.

Because RF ablation may generate significant heat, which if notcarefully monitored and/or controlled can result in proteindenaturation, blood coagulation, excess tissue damage, such as steampop, tissue charring, and the like, it is desirable to monitor thetemperature of the ablation assembly. It is further desirable to includea mechanism to irrigate the target area and the device withbiocompatible fluids, such as saline solution. This irrigation mitigatesexcess, unwanted tissue damage and mitigates rising temperatures fromthe electrode assembly, which potentially causes premature shutdown ofthe ablative assembly during operation. However, introduction of thisirrigation solution may inhibit the ability to accurately monitor and/orcontrol the temperature of the ablation assembly during use.

There are typically two classes of irrigated electrode catheters, openand closed irrigation catheters. Closed ablation catheters typicallycirculate a cooling fluid within the inner cavity of the electrode. Openablation catheters, on the other hand, typically deliver the coolingfluid through open orifices on the electrode. Examples of these knowncatheters include the THERMOCOOL brand of catheters marketed and sold byBiosense-Webster. The current open irrigated ablation catheters use theinner cavity of the electrode, or distal member, as a manifold todistribute saline solution. The saline thus flows directly through theopen orifices of the distal electrode member. This direct flow throughthe distal electrode tip lowers the temperature of the distal tip duringoperation, rendering accurate monitoring and control of the ablativeprocess more difficult.

In these open electrode irrigated catheters, it has been determined thatinsulating the irrigation channels from the ablation electrode isbeneficial. One such example was published on or around March 2005 in anarticle entitled “Saline-Irrigated Radiofrequency Ablation Electrodewith Electrode Cooling,” by Drs. Wittkampf and Nakagawa, et al., thecontent of which is hereby incorporated by reference in its entirety.Similarly, the content of PCT International Publication No. WO05/048858, published on Jun. 2, 2005, is hereby incorporated byreference in its entirety.

BRIEF SUMMARY OF THE INVENTION

The present invention provides for significant improvements over knownirrigation catheters, including those disclosed by Drs. Wittkampf andNakagawa, et al., by providing a multiple piece irrigated ablationelectrode assembly that provides the advantages of irrigating the targetarea and the electrode assembly while simultaneously improving theoperation, temperature response, temperature monitoring and/or controlmechanisms of the ablation assembly, so as to prevent unwanted,unnecessary tissue damage. The present invention further provides forablation electrode assemblies that are easier to manufacture andassemble than known irrigated ablation electrode assemblies.

The present invention is directed to improved irrigated ablationelectrode assemblies and methods useful in conjunction with irrigatedcatheter and pump assemblies and RF generator assemblies designed tomonitor and control the ablation process while minimizing bloodcoagulation and unnecessary tissue damage.

The present invention provides for an irrigated ablation electrodeassembly for use with an irrigated catheter device comprising a proximalmember having at least one passageway for a fluid and at least oneoutlet for the fluid; and a distal member having at least onetemperature sensor located within the distal member, wherein thepassageway and the at least one outlet are spaced from the at least onetemperature sensor by at least a portion of a poor thermally conductivematerial.

In one embodiment, the proximal member is comprised of a poor thermallyconductive material selected from the group consisting of HDPE,polyimide, polyaryletherketones, polyetheretherketones, polyurethane,polypropylene, oriented polypropylene, polyethylene, crystallizedpolyethylene terephthalate, polyethylene terephthalate, polyester,ceramics, and plastics such as Dekin®, and mixtures thereof. The distalmember is comprised of an electrically, and potentially thermally,conductive material selected from the group consisting of platinum,gold, iridium, palladium, stainless steel, and mixtures thereof.

In another embodiment, the proximal member and the distal member arecomprised of an electrically, and potentially thermally, conductivematerial selected from the group consisting of platinum, gold, iridium,palladium, stainless steel, and mixtures thereof. The material for theproximal member need not be the same as the distal member. In thisembodiment, the distal member and the proximal member are separated by apoor thermally conductive material and are electrically connected thoughan electrical connection device. The proximal member is thenelectrically connected to an electrical source through an electricalconnection device.

The present invention further includes an irrigated ablation electrodeassembly comprising an electrode member comprising at least onetemperature sensor; and an irrigation member having at least one conduitfor a fluid, the at least one conduit being thermally insulated from thedistal member.

In one embodiment, the irrigation member is comprised of a poorthermally conductive material selected from the group consisting ofHDPE, polyimide, polyaryletherketones, polyetheretherketones,polyurethane, polypropylene, oriented polypropylene, polyethylene,crystallized polyethylene terephthalate, polyethylene terephthalate,polyester, ceramics, and plastics such as Delrin®, and mixtures thereof.The electrode member is comprised of an electrically, and potentiallythermally, conductive material selected from the group consisting ofplatinum, gold, iridium, stainless steel, and mixtures thereof.

In another embodiment, the irrigation and electrode members arecomprised of an electrically, and potentially thermally, conductivematerial selected from the group consisting of platinum, gold, iridium,palladium, stainless steel, and mixtures thereof, but they need not becomprised of the same material. In this embodiment, the electrode memberand the irrigation member are separated by a poor thermally conductivematerial and are electrically connected though an electrical connectiondevice. The irrigation member is then electrically connected to anelectrical source through an electrical connection device.

In accordance with embodiments of the present invention, the at leastone passageway or conduit of the proximal or irrigation member extendsat either an angle substantially perpendicular to a horizontal, i.e.,longitudinal, axis of the proximal or irrigation member, or axiallytowards the distal member at an angle substantially less thanperpendicular to a longitudinal axis of the proximal or irrigationmember, between approximately 15 and 70 degrees, preferablyapproximately 30 to 45 degrees, most preferably approximately 30degrees.

Further, the ablation electrode assembly may also include a second and,optionally, a third poor thermally conductive material disposed betweenthe proximal or irrigation member and the distal or electrode memberselected from the group consisting of HDPE, polyimide,polyaryletherketones, polyetheretherketones, polyurethane,polypropylene, oriented polypropylene, polyethylene, crystallizedpolyethylene terephthalate, polyethylene terephthalate, polyester,ceramics, and plastics such as Delrin®, and mixtures thereof. Theablation electrode assembly may also include a second and, optionally, athird thermally conductive material disposed between the temperaturesensor(s) and the distal or electrode member.

The present invention further includes methods for improved measurementand control of a temperature of an irrigated ablation electrode assemblyor a target site and minimization of coagulation and excess tissuedamage at and around the target site comprising the following steps:providing an ablation electrode assembly having at least one temperaturesensor disposed within a distal or electrode member of the irrigatedelectrode assembly and having a proximal or irrigation member separatefrom the distal member; providing an irrigation pathway within theproximal member for delivery of a fluid to an external portion of theablation electrode assembly and the target site to minimize excesstissue damage during operation of the ablation electrode assembly;providing a poor thermally conductive material between the irrigationpathway and the distal member to accurately measure the temperature ofthe distal member during operation of the ablation electrode and duringdelivery of the fluid to the target site. The methods further includethe step of providing a second and, optionally, a third poor thermallyconductive material disposed between the irrigation pathway and thedistal member. The methods also include the step of providing athermally conductive material between the at least one temperaturesensor and the distal member.

Additional methods for improved measurement and control of a temperatureof an irrigated ablation electrode assembly or a target site andminimization of coagulation and excess tissue damage at and around thetarget site during operation comprise the following steps: obtaining anablation electrode having at least one temperature sensor disposed witha distal member and a passageway for distribution of a fluid to thetarget site, the passageway being insulated from the temperature sensor;irrigating the target site during operation of the ablation electrode bypassing the fluid through the passageway; monitoring the temperaturesensor(s) during operation of the ablation electrode; and maintainingoperational parameters so as to minimize excess tissue damage duringoperation of the ablation electrode. The methods further contemplatedelivering the fluid to an outer portion of the distal member.

Further methods for improved assembly of irrigation electrode assembliesare provided comprising the following steps: providing a distal memberhaving at least one locking member extending from an inner portion of anopen end of the distal member and extending a predetermined lengthangularly outward from the open end and terminating in a lip extendingtoward the central axis of the distal member; providing a proximalmember having at least one locking member extending from an innerportion of an open end of the distal member extending a predeterminedlength angularly outwardly from the open end, terminating in a lipextending toward the central axis of the distal member; and pressing thedistal member and the proximal member together. These methods may alsoinclude the step of providing a poor thermally conductive adhesivebetween the proximal member and the distal member, whereby when theproximal member and the distal member are pressed together, a furtherchemical bond is achieved.

A technical advantage of the present invention is that the electrodeassembly thermally separates the cooling irrigation fluid from thedistal member, and more particularly the temperature sensingmechanism(s) within the distal member, thereby allowing for improvedtemperature control and/or monitoring while simultaneously allowing forirrigation of the electrode assembly and the target areas to minimizecoagulation and unwanted tissue damage. The separation of the coolingfluid from the temperature sensing mechanisms further allows for bettermonitoring of rising temperature of the electrode assembly duringoperation, as well as other tell-tale factors of over-ablation oftargeted tissue areas.

Another advantage of the present invention is improved manufacturabilityof insulated, irrigated ablation electrode assemblies. The multiplepiece design of the ablation electrode assembly allows for ease ofmanufacture and assembly of ablation electrode catheters over knownelectrode assemblies.

Yet another advantage of the invention is the ability to easilymanufacture and assemble any number of known sizes of irrigatedelectrode assemblies, including 2 mm, 2½ mm and 4 mm assemblies.

The foregoing and other aspects, features, details, utilities, andadvantages of the present invention will be apparent from reading thefollowing description and claims, and from reviewing the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an ablation electrode assembly 10according to a first embodiment of the present invention in conjunctionwith an irrigated catheter assembly 12 operably connected to an RFgenerator assembly 14 and a pump assembly 15.

FIG. 2 is an enlarged, isometric view of the ablation electrode assembly11 according to the first embodiment of the present invention operablyconnected to an irrigated catheter assembly 12.

FIG. 3 is a cross-sectional view of an ablation electrode assembly 13according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view of the ablation electrode assembly 11of FIG. 2 taken along line 4-4 of FIG. 2.

FIG. 5 is a cross-sectional view similar to FIGS. 3 and 4 of an ablationelectrode assembly 19 according to a third embodiment of the presentinvention.

FIG. 6 is a cross-sectional view similar to FIGS. 3-5 according to afourth embodiment of the present invention.

FIG. 7 is an isometric, exploded view of an ablation electrode assemblyaccording to a fifth embodiment of the present invention.

FIG. 8 is a cross-sectional view taken along line 8-8 of FIG. 7.

FIGS. 9, 10 and 11 graphically depict bench test results for ablationelectrode assemblies.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In general, the instant invention relates to irrigated ablationelectrode assemblies 10, 11, 13, 19, 21, and 23, and to methods ofmanufacturing and using such irrigated ablation electrode assemblies.For purposes of this description, similar aspects among the variousembodiments described herein will be referred to by the same referencenumber. As will be appreciated, however, the structure of the variousaspects may be different among the various embodiments.

The ablation electrode assembly may comprise part of an irrigatedablation catheter 12 assembly, operably connected to a pump assembly 15and a RF generator assembly 14 which serves to facilitate the operationof ablation procedures through monitoring any number of chosen variables(e.g., temperature of the ablation electrode, ablation energy, andposition of the assembly), assist in manipulation of the assembly duringuse, and provide the requisite energy source delivered to the electrodeassembly 10. The present embodiments describe RF ablation electrodeassemblies and methods, but it is contemplated that the presentinvention is equally applicable to any number of other ablationelectrode assemblies where the temperature of the device and thetargeted tissue areas is a factor during the procedure.

FIG. 1 is a general perspective view of an irrigated ablation catheterassembly having a RF generator assembly 14 and a fluid pump assembly 15operably connected to an irrigation catheter 12 assembly having anirrigated electrode assembly 10 according to the present inventionoperably attached thereto. The structural and functional features of thecatheter assembly 12 and the RF generator assembly 14 and pump assembly15 are well-known to those of skill in the art. For example, the RFgenerator assembly could be an IBI-1500T RF Cardiac Ablation Generatoravailable from Irvine Biomedical, Inc. in Irvine, Calif. 92614. The RFgenerator assembly could also be any other known assembly, including,for example, a Stockert RF generator available from Biosense, or one ofthe Atakr® series of RF generators available from Medtronic. The pumpassembly can be any known assembly, including fixed volume rollingpumps, variable volume syringe pumps, and any other pump assembly knownto those of skill in the art. FIGS. 2-8, discussed in more detail below,exemplify various embodiments of the irrigated ablation electrodeassembly 10 according to the present invention.

FIG. 2 is an isometric view of an ablation electrode assembly 11connected to an irrigated ablation catheter assembly 12 having a fluiddelivery tube 16 therein. The ablation electrode assembly 11 generallycomprises an irrigation member 20 and an ablation electrode member 18.The orientation of the members 18, 20 are generally such that theablation electrode assembly 18 is situated at the distal end of theassembly with the irrigation member 20 located at the proximal end ofthe assembly, although it is conceivable the orientation could bereversed. The proximal member 20 has at least one passageway 24 (notshown) and at least one outlet 22 for delivery of a fluid to targetedtissue areas and the outside of the electrode assembly 11. The distalmember 18 further comprises at least one temperature sensing mechanism26 (not shown) disposed therein and operably connected to the RFgenerator assembly 14. The distal member 18 is comprised of anyelectrically, and potentially thermally, conductive material known tothose of ordinary skill in the art for delivery of ablative energy totarget tissue areas. Examples of the thermally conductive materialinclude gold, platinum, iridium, palladium, stainless steel, and anymixtures thereof. Moreover, there are a number of electrode designscontemplated within the scope of the present invention including tipelectrodes, ring electrodes, and any combination thereof.

In general accordance with the embodiments described herein, the fluidpassageway(s) 24 and outlet(s) 22 are separated from the distal member18, and accordingly the temperature sensing mechanism 26, by at leastone poor thermally poor thermally conductive material. A poor thermallypoor thermally conductive material is one with physical attributes thatdecreases heat transfer from the passageway(s) 24 to the distal member18 by about 10% or more, and more preferably by about 25% or moremeasured by known methods to one of ordinary skill in the art. Inparticular embodiments, materials that decreased heat transfer by morethan approximately 75% performed favorably. It is further contemplatedthat a poor thermally poor thermally conductive material could havephysical attributes that decrease heat transfer less than about 10%,provided that the remaining structural components are selected with theappropriate characteristics and sensitivities to maintain adequatemonitoring and control of the process. Thus, while these properties arepreferred, the poor thermally conductive material may be any materialknown to one of skill in the art consistent with the spirit of theinvention. Examples of poor thermally conductive materials useful inconjunction with the present invention include, but are not limited to,HDPE, polyimides, polyaryletherketones, polyetheretherketones,polyurethane, polypropylene, oriented polypropylene, polyethylene,crystallized polyethylene terephthalate, polyethylene terephthalate,polyester, ceramics, and plastics such as Delrin®, and mixtures thereof.

As shown in more detail with respect to specific embodiments below, thepoor thermally conductive material may be the material comprising theproximal member 20, or the distal member 18, a separate material fromthe proximal member 20 and the distal member 18, or any combinationthereof. Additionally, the passageway(s) 24 and outlet(s) 22 defined bythe proximal member 18 may also be separated longitudinally from the end46 of the distal member 18 thereby providing the benefit of insulatingthe passageway(s) 24 from the temperature sensor(s) 26 for improvedtemperature monitoring of the ablated target area during operation. Thepoor thermally conductive material, and the separation from the end 46of the distal member 18, serve individually, and cooperatively, tominimize the effect of the lower temperature of the fluid deliveredthrough the passageway(s) 24 and outlet(s) 22 from the temperaturesensing mechanism(s) 26 within the distal member 18. The separation ofthe passageway(s) 24 and outlet(s) 22 from the distal member 18, andmore particularly the temperature sensing mechanism 26 to facilitate thedual purposes of (1) effectively irrigating the electrode assembly 10and the targeted tissue area to minimize coagulation and unwanted tissuedamage and (2) effectively controlling the operation of the ablationelectrode assembly 10 in accordance with objects of the presentinvention.

FIG. 3 is a cross-sectional view of an embodiment of the ablationelectrode assembly 13. FIG. 3 describes what is known to those in theart as a 2½ mm (length) ablation electrode assembly 10. A 2½ mm ablationelectrode assembly 10 is often beneficial because it requires less power(around 10-20 W, as compared to around 20-40 W for a 4 mm assembly).However, it is contemplated that any size ablation electrode assembly13, including a 4 mm assembly, is equally technically acceptable. Ininstances where a larger ablation area is desired to provide fordifferent spatial orientation of the electrode assembly 13, for exampleas shown in FIGS. 5 and 6 below, a larger electrode surface area can beaccommodated, while still yielding the desirable separation between thecooling passageways 24 and the temperature sensing mechanism 26.

As shown in FIG. 3, an ablation electrode assembly 13 is connected to anirrigation catheter assembly 12 having a fluid delivery tube 16. Theablation electrode assembly 13 comprises a proximal member 20, ormanifold, a distal member 18, and a temperature sensing mechanism 26operably connected to the RF generator assembly 14 (not shown). In thisembodiment, the proximal member 20 itself is comprised of a poorthermally conducting material that serves to insulate the fluid from theremaining portions of the assembly 13. Preferably the proximal member 20is made from a poor thermally conductive polymer, more preferably from apolyether ether ketone (“PEEK”) because of this material's combinationof thermal and physical properties. The proximal member 20 is configuredto receive the fluid tube 16 of the catheter assembly 12 and comprises aplurality of passageways 24 extending from a central axis 28 of theassembly 13 axially toward the outer portion of the proximal member 20terminating in corresponding outlets 22. Preferably, the plurality ofpassageways 24 are equally distributed around the proximal member 20 soas to provide equal distribution of fluid to the targeted tissue areaand the outside of the assembly 13. The passageway 24 may be a single,annular passageway, or a number of individual passageways equallydistributed around the proximal member 20. In this embodiment, thepassageways 24 are at an angle substantially perpendicular to thehorizontal axis 28 of the assembly 13. In operation, fluid is pumpedthrough the delivery tube 16 and passes through the passageways 24 andthrough the outlets 22 where it contacts with targeted tissue areas andthe outside portion of the ablation electrode assembly 13.

The proximal member 20 is further configured to extend a portion 48 intothe distal member 18 and has a pathway 50 for passage of the operableconnection of the temperature sensing mechanism 26 within the distal tip18. In this embodiment, this path 50 is shown extending substantiallythrough the middle of the proximal member 20, however, this path 50 canbe located anywhere within or outside the proximal member 20. Theresulting cross-sectional shape is substantially cross-shaped, in whichthe fluid passageways 24 and conduits 22 are isolated from otherportions of the assembly 13 by the proximal member 20.

The distal member 18 of the ablation electrode assembly 13 has agenerally cylindrical shape terminating in a semispherical end. Thedistal member 18 is configured to accept a portion 48 of the proximalmember 20 for attachment thereto. The distal member 18 may be connectedto the proximal member 20 by any known mechanism (not shown) includingadhesives, press-fit configurations, snap-fit configurations, or anyother mechanism known to one of skill in the art.

The distal member 18 further contains at least one temperature sensingmechanism 26 disposed therein for measurement and control of theassembly 13 and targeted tissue areas during operation. It is furthercontemplated that additional temperature sensing mechanisms (not shown)can be utilized for further control and monitoring of the temperature ofthe assembly 13 at various additional locations. For purposes of thepresent invention, the temperature sensing mechanism(s) 26 can be anymechanism known to one of skill in the art, including for example,thermocouples or thermistors. In a further embodiment, the temperaturesensing mechanism 26 is surrounded, or encapsulated, by a secondthermally conductive and electrically non-conductive material 30. Thisthermally conductive and electrically non-conductive material 30 servesto hold the temperature sensing mechanism 26 in place within the distaltip 18 and provides excellent heat exchange between the temperaturesensing mechanism 26 and the distal member. This material 30 may becomprised of a number of materials known to one of skill in the art,including for example, thermally conductive resins, epoxies, or pottingcompounds, such as the material sold under the trademark STYCAST 2651MM.

FIG. 4 is a cross-sectional view of another embodiment of the ablationelectrode assembly 11, similar to that described above and shown in FIG.3. In this embodiment, however, the fluid delivery conduits 24, orpassageways, extend at an angle substantially less than perpendicular tothe horizontal axis 23. Angling of the passageways 24 away fromperpendicular, but less than parallel, further assists in the deliveryof the fluid to the targeted tissue areas, further decreases the risk ofcoagulation of the bodily fluids during ablation procedures, and allowsfor improved measurement and control of the ablation assembly 11 duringoperation. Preferably, the passageways 24 extend at an angle betweenapproximately 20 and 70 degrees, more preferably at an angle betweenapproximately 30 and 60 degrees, and most preferably at an angle ofapproximately 30 degrees. It is also contemplated that the passagewaysmay be further angled in a second dimension, such that the passagewaysand orifices are configured to provide fluid to the external portion ofthe assembly in a swirling, or helical fashion. This configurationserves to keep the fluid in closer proximity to the electrode assembly,thereby further preventing against coagulation during operation.

Again, in this embodiment, the temperature sensing mechanism 26 issurrounded, or encapsulated, by a second thermally conductive andelectrically non-conductive material 30. This thermally conductive andelectrically non-conductive material 30 serves to hold the temperaturesensing mechanism 26 in place within the distal tip 28 and providesexcellent heat exchange between the temperature sensing mechanism 26 andthe distal member. This material 30 may be comprised of a number ofmaterials known to one of skill in the art, including for example,thermally conductive resins, epoxies, or potting compounds, such as thematerial sold under the trademark STYCAST 2651 MM.

FIG. 5 is a cross-sectional view of yet another embodiment of theablation electrode assembly according to the present invention. Inaccordance with this embodiment, the electrode assembly 19 comprises adistal member 18 configured to house at least one temperature sensingmechanism 26 (only one shown) and a proximal member 20 having a fluiddelivery conduit 17, at least one passageway 24 and at least one orifice22 for delivery of a fluid to target tissue areas and the outside of theablation electrode assembly 19. The fluid delivery conduits 24, orpassageways, extend axially away from the horizontal axis 28 of theassembly 19 at an angle of approximately 45 degrees from perpendicular.In preferred embodiments, an angle of 30 degrees also peformedfavorably. Such angled passageways 24 are preferred because they furtherdecrease coagulation around the target tissue areas during operation.The proximal member 20 is configured to accept a fluid delivery tube 16from an irrigation catheter 12 and is further configured to mate withthe irrigation catheter assembly 12 and the fluid pump assembly 15.Consistent with the other embodiments, the proximal member 20 can beattached to the catheter assembly 12 by any known mechanism, includingsnap-fit, pressure fit, physically or chemically bonded, or anycombination thereof.

In this embodiment, the proximal member 20 and the distal member 18 areboth comprised of electrically, and possibly thermally, conductivematerials. In this embodiment, both the proximal 20 and distal 18members are electrically connected to an ablation power source (notshown) and are capable of ablating targeted tissue areas. The membersmay be made of the same material, or may be comprised of differentmaterials.

The proximal member 20 and distal member 18 are separated from eachother in this embodiment through at least one poor thermally conductivematerial 32. Additionally, the proximal member 20 and the distal member18 may be bonded together using a thermally-poor conductive adhesive 32known to those of skill in the art. In this instance, the proximal 20and distal 18 members are electrically connected through any electricalconnection device 34, such as an electrically conductive wire. Theproximal member 20 is electrically connected to an energy source (notshown) through another electrical connection device 36. The result ofthis configuration provides the benefit of an increased ablationelectrode surface area (encompassing both the distal and proximalmembers), where the proximal member 20 is generally cooler than thedistal member 18. At least one temperature sensing mechanism 26 isplaced within the distal member 18. The temperature sensing mechanism 26may be further surrounded, or encapsulated, by another thermallyconductive, electrically non-conductive, material 30. This thermallyconductive, electrically non-conductive, material serves to hold thetemperature sensing mechanism 26 in place within the distal tip 18 andprovides excellent heat exchange between the temperature sensingmechanism 26 and the distal member. This material 30 may be comprised ofa number of materials known to one of skill in the art, including forexample, thermally conductive resins, epoxies, or potting compounds,such as the material sold under the trademark STYCAST 2651 MM. Byplacing the temperature sensing mechanism 26 within the distal member18, displaced from the proximal member 20, improved temperaturemeasurements and control are still maintained, while allowing fordecreased coagulation and unnecessary tissue damage through irrigation.This particular configuration enables the use of a number of differentsizes of ablation electrodes 10, including 4 mm electrodes, ringelectrodes, and combinations thereof

FIG. 6 is a cross-section view of yet another embodiment of the presentinvention, similar to that described above and shown in FIG. 5. In thisembodiment, the distal member 18, or the proximal member 20 comprisesanother poor thermally conductive material 32 displaced between theproximal member 20 and the distal member 18. This additional poorthermally conductive material 32 provides further insulation of thetemperature sensing mechanism(s) 26 thereby further allowing forimproved temperature measurements and control of the ablation assembly21, while allowing for decreased coagulation and unnecessary tissuedamage through irrigation. Similar to the embodiment described above andshown in FIG. 5, the distal member 18 and proximal member 20 may bechemically bonded together with thermally poor conductive adhesivesknown to those in the art. In this instance, the distal member 18 andthe proximal member 20 are electrically connected through an electricalconnection device 34, such as a wire. In the instance where such anadhesive is not utilized, the electrical connection between the proximal20 and distal 18 members is accomplished via direct contact.

FIG. 7 is an isometric, exploded view of yet another embodiment of thepresent invention, similar to that described above and shown in FIGS. 5and 6. In this embodiment, the distal member 18 and the proximal member20 are cooperatively configured to facilitate a snap-fit, orpressure-fit connection assembly. As an example, the distal member 18 isconfigured with at least one locking member 42 extending from an innerportion 52 of the open end of the distal member 18 extending apredetermined length angularly outward from the open end, terminating ina lip 54 extending toward the central axis of the distal member 18.Cooperatively, the proximal end 20 has at least one locking member 40extending from an inner portion 56 of the open of the distal member 20extending a predetermined length angularly outward from the open end,terminating in a lip 58 extending toward the central axis of theproximal member 20. FIG. 8 shows a cross-sectional view taken alongsection 8 of FIG. 7. When lined up and pressed together, the distalmember 18 and the proximal members 20 thereby form a snap-fit assembly.In addition to the embodiment shown in FIG. 8, any number of lockingmembers 40, 42 can be utilized, including both locking members 40, 42having a single annular rib 54, 58 extending substantially around theinside of the member 40, 42. It is also contemplated that the lockinglips 54, 58 could be eliminated to form a pressure-fit connectionassembly. It is further contemplated that in addition to the mechanicalassemblies, the distal 18 and proximal 20 members can be furtherchemically bonded with a poor thermally conductive adhesive 32 known tothose of skill in the art. Utilizing such a configuration provides theadditional benefit of eliminating the need for an electrical connectionwire 34, while simultaneously allowing for additional insulation andstrength of connection between the members 18, 20 through use of a poorthermally conductive adhesive 32, for the electrical connection isserved by the touching of the lips 54, 58 of the respective members 18,20.

In addition to the preferred embodiments discussed above, the presentinvention contemplates methods for improved measurement and control of atemperature of an irrigated ablation electrode assembly 23 or a targetsite and minimization of coagulation and excess tissue damage at andaround the target site. According to one method, an ablation electrodeassembly 23 is provided, having at least one temperature sensor 26disposed within a distal member 18 of the irrigated electrode assembly23 and having a proximal member 20 separate from the distal member 18. Aseparate irrigation pathway 24 is provided within the proximal member 20for delivery of a cooling fluid to an external portion of the ablationelectrode assembly 23 and the target site to minimize excess tissuedamage during operation of the ablation electrode. A poor thermallyconductive material is also provided between the irrigation pathway 24within the distal member 18 thereby allowing for improved measurement ofthe temperature of the ablation electrode assembly 23 during operation,while simultaneously allowing for the benefits of irrigation of thetarget site and external portions of the electrode assembly 10, such asminimizing tissue damage, such as steam pop, preventing rising impedanceof the ablation assembly, and minimizing blood coagulation.Additionally, a second, optionally a third, poor thermally conductivematerial 32 can be provided between the irrigation pathway 24 within theproximal member 20 and the temperature sensing mechanism 26 furtherenhancing the measurement and control of temperature of the electrodeassembly while simultaneously allowing for the benefits of irrigation ofthe target site and external portions of the electrode assembly 23.

Another method for improved measurement and control of a temperature ofan irrigated ablation electrode assembly 23 or a target site andminimization of coagulation and excess tissue damage at and around thetarget site during operation comprises the steps of obtaining anablation electrode 10 having a temperature sensor 26 disposed with adistal member 18 and a passageway 24 for distribution of a fluid to thetarget site, the passageway 24 being insulated from the temperaturesensor 26; irrigating the target site during operation of the ablationelectrode by passing the fluid through the passageway 24; monitoring thetemperature sensor 26 during operation of the ablation electrode 10; andmaintaining operational parameters so as to minimize excess tissuedamage during operation of the ablation electrode. This method furthercontemplates the step of delivering the fluid to an outer portion of thedistal member 18.

The present invention further provides for yet additional improvedmethods of assembly of irrigation electrode assemblies 23, by providingdistal member 18 and a proximal member 20 cooperatively configured tofacilitate a snap-fit, or pressure-fit connection assembly. Inaccordance with this method, a distal member 18 is provided having atleast one locking member 42 extending from an inner portion 52 of theopen end of the distal member 18 extending a predetermined lengthangularly outward from the open end, terminating in a lip 54 extendingtoward the central axis of the distal member 18. Cooperatively, aproximal member 20 is provided having at least one locking member 40extending from a portion 56 of the proximal member 20 extending apredetermined length angularly outward from the end 56, terminating in alip 58 extending toward the central axis of the proximal member 20. Thecomplete assembly 23 is configured by pressing the distal member 18 andthe proximal member 20 together until they snap into place.Additionally, the contemplated methods further comprise providing a poorthermally conductive 32 adhesive between the proximal member 20 and thedistal member 18, such that when snapped into place, a further chemicalbond is achieved, that further insulates the fluid passageways 24 fromthe temperature sensing mechanism(s) 26 within the distal member 18.

EXAMPLES

Two designs in accordance with the present invention were prepared andtested against a design representative of known irrigated ablationcatheters and a control design representative of known non-insulatedirrigated ablation catheter.

Design A represents an irrigated electrode assembly 10 as shown in FIG.3 having fluid passageways 24 configured substantially perpendicular tothe horizontal axis of the manifold 20. The manifold 20 of Design A wasmade of PEEK, machined into the configuration described in FIG. 3. Thedistal member 18 was comprised of stainless steel and contained a singlethermocouple 26 disposed therein encapsulated by STYCAST.

Design B represents an irrigated electrode assembly 10 similar in designto FIG. 4 having fluid passageways 24 configured at an angle ofapproximately 45 and 30 degrees from perpendicular to the horizontalaxis of the manifold 20. The manifold 20 of Design A was made of PEEK,machined into the configuration described in FIG. 4. The distal member18 was comprised of stainless steel and contained a single thermocouple26 disposed therein encapsulated by STYCAST.

Design C represents a single piece irrigated electrode assembly havingindividually insulated irrigation pathways extending both axially andlongitudinally to the distal tip. Design C was prepared in accordancewith the insulated ablation electrode assembly disclosed in Drs.Wittkampf and Nakagawa's publication entitled “Saline-IrrigatedRadiofrequency Ablation Electrode with Electrode Cooling” cited above,with the exception that the passageways extending axially from thehorizontal axis of the assembly were not separately insulated. Thisresulted in an insulated ablation assembly in which approximately 85% ofthe irrigation pathways were insulated from the distal member. Thepathways were insulated using PEEK tubing.

The Control design represents a non-insulated, single piece irrigatedelectrode assembly having irrigation pathways extending both axially andlongitudinally to the distal tip. The structure of the distal member wasprepared in accordance with the insulated ablation electrode assemblydisclosed in Drs. Wittkampf and Nakagawa's publication entitled“Saline-Irrigated Radiofrequency Ablation Electrode with ElectrodeCooling” cited above, without any corresponding insulation surroundingthe individual cooling fluid passageways.

Bench tests were conducted on experimental fresh cow cardiac tissuetested in a 37 degree Celsius saline water bath for a period of 30seconds and 60 seconds, using the various irrigated ablation catheterassemblies operating at 10 W, 100 ohms impedance, 80 degrees Celsius,and simulated circulatory conditions of from 0.125 L/min to 1 L/min. Thesaline solution was delivered with an adjustable syringe pump thatallowed for varying flow rates of saline of from 8 ml/min to 16 ml/min.The temperature of the end of the distal member and the tissuetemperature were monitored and plotted against time.

The results of the experiments are shown in FIGS. 9, 10 and 11. FIG. 9shows only the temperature of the distal member of the Designs A 60, B62, C 64 and the Control 66. As seen from FIG. 9, the temperature of theControl 66, non-insulated ablation electrode assembly resulted in thelargest temperature measurement disparity, lowering the measuredtemperature from the 80 degrees Celsius operating temperature 68, toapproximately 41 degrees Celsius. This substantial difference intemperature represents the difficulties in monitoring and controllingthe ablation process that is commonly associated with non-insulateddesigns. Design C 64 succeeded in decreasing the temperature disparityapproximately 8 degrees Celsius over the non-insulated design 66.Designs A 60 and B 62, however, provided significantly improvedreduction of the temperature disparity to approximately 62 degreesCelsius and 58 degrees Celsius, respectively. The difference intemperature disparity between Designs A 60 and B 62 and C 64 and theControl 66 represent significant benefits for controlling and monitoringablation procedures.

FIG. 10 shows the results of a second experiment measuring thetemperature of the distal member and also the measured temperature ofthe corresponding tissue 61, 63, 65, respectively, being tested. Again,Designs A 60 and B 62 resulted in a much closer disparity between theactual tissue temperatures 61, 63 and distal member as compared toDesign C 64. This further substantiates the structural advantages of theembodiments of the present invention compared to known insulated andnon-insulated irrigated ablation electrode assemblies.

FIG. 11 identifies the measured temperature of the tissue and comparesDesign B to the Control design under the same test conditions. Agains,as shown in FIG. 11, the temperature of the non-insultated tip of theControl design was significantly lower than the insulated tip of DesignB.

Other embodiments and uses of the devices and methods of the presentinvention will be apparent to those skilled in the art fromconsideration of the specification and practice of the inventiondisclosed herein. The specification and examples should be consideredexemplary only with the true scope and spirit of the invention indicatedby the following claims. As will be easily understood by those ofordinary skill in the art, variations and modifications of each of thedisclosed embodiments can be easily made within the scope of thisinvention as defined by the following claims.

All directional references (e.g., upper, lower, upward, downward, left,right, leftward, rightward, top, bottom, above, below, vertical,horizontal, clockwise, and counterclockwise) are only used foridentification purposes to aid the reader's understanding of the presentinvention, and do not create limitations, particularly as to theposition, orientation, or use of the invention. Joinder references(e.g., attached, coupled, connected, and the like) are to be construedbroadly and may include intermediate members between a connection ofelements and relative movement between elements. As such, joinderreferences do not necessarily infer that two elements are directlyconnected and in fixed relation to each other. It is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative only and not limiting.Changes in detail or structure may be made without departing from thespirit of the invention as defined in the appended claims.

1-33. (canceled)
 34. A method for improved measurement and control of a temperature of an irrigated ablation electrode assembly or a target site and minimization of coagulation and excess tissue damage at and around the target site comprising the steps of: providing an ablation electrode assembly having at least one temperature sensor disposed within a distal member of the irrigated electrode assembly and having a proximal member separate from the distal member; providing an irrigation pathway within the proximal member for delivery of a fluid to an external portion of the ablation electrode assembly and the target site to minimize excess tissue damage during operation of the ablation electrode; providing a poor thermally conductive material between the irrigation pathway and the distal member to accurately measure the temperature of the distal member during operation of the ablation electrode and during delivery of the fluid to the target site.
 35. The method of claim 34 further comprising the step of providing a second poor thermally conductive material disposed between the irrigation pathway and the distal member.
 36. The method of claim 34 further comprising the step of providing a thermally conductive material between the at least one temperature sensor and the distal member.
 37. A method for improved measurement and control of a temperature of an irrigated ablation electrode assembly or a target site and minimization of coagulation and excess tissue damage at and around the target site during operation comprising the steps of: obtaining an ablation electrode having at least one temperature sensor disposed with a distal member and a passageway for distribution of a fluid to the target site, the passageway being insulated from the temperature sensor; irrigating the target site during operation of the ablation electrode by passing the fluid through the passageway; monitoring at least one temperature sensor during operation of the ablation electrode; and maintaining operational parameters so as to minimize excess tissue damage during operation of the ablation electrode.
 38. The method of claim 37 further comprising the step of delivering the fluid to an outer portion of the distal member. 39-40. (canceled)
 41. The method of claim 34 wherein providing an ablation electrode assembly comprises providing an electrically conductive distal member having a first end and a second end.
 42. The method of claim 41 wherein the electrically conductive distal member is fabricated from a material selected from the group comprising platinum, gold, iridium, stainless steel, palladium and mixtures thereof.
 43. The method of claim 41 wherein providing the irrigation pathway comprises providing the pathway such that the pathway extends radially from a central axis of the irrigated ablation electrode assembly toward an outer portion of the proximal member to an outlet.
 44. The method of claim 43 further comprising disposing the distal member and the proximal member such that one of the first end and the second end of the distal member is configured to receive only a portion of the proximal member such that the portion of the proximal member is disposed internally relative to the distal member.
 45. The method of claim 44 wherein providing the irrigation pathway comprises providing the pathway and the outlet such that the pathway outlet are not positioned longitudinally between the first and second ends of the distal member.
 46. The method of claim 44 wherein providing the irrigation pathway comprises separating the pathway and the outlet longitudinally from the distal member and the at least one temperature sensor.
 47. The method of claim 34 wherein providing the irrigation pathway comprises providing the pathway such that the pathway extends at an angle substantially perpendicular to a horizontal axis of the proximal member.
 48. The method of claim 34 wherein providing the irrigation pathway comprises providing the pathway such that the pathway extends axially towards the distal member at an angle substantially less than perpendicular to a horizontal axis of the proximal member.
 49. The method of claim 48 wherein providing the irrigation pathway comprises providing the pathway so as to extend axially towards the distal member at an angle between approximately 20 and approximately 70 degrees from an angle perpendicular to the horizontal axis of the proximal member.
 50. The method of claim 37 wherein irrigating and monitoring are performed simultaneously.
 51. The method of claim 37 wherein maintaining operational parameters comprises facilitating operation of the ablation electrode according to the monitored temperature.
 52. The method of claim 37 further comprising monitoring at least one of an ablation energy and a position of the irrigated ablation electrode assembly.
 53. The method of claim 37 wherein the at least one temperature sensor is a first temperature sensor disposed at a first location, the method further comprising monitoring a second temperature sensor disposed at a second location during operation of the ablation electrode.
 54. The method of claim 53 wherein maintaining operational parameters is performed in accordance with the monitored first and second temperature sensors.
 55. A method for improved measurement and control of a temperature of an irrigated ablation electrode assembly, the method comprising: providing an ablation electrode assembly having at least one temperature sensor disposed within a first member of the irrigated electrode assembly and having a second member separate from the first member; providing an irrigation pathway within the second member for delivery of a fluid to an external portion of the ablation electrode assembly and a target site during operation of the ablation electrode assembly; providing a poor thermally conductive material between the irrigation pathway and the first member to accurately measure the temperature of the first member during operation of the ablation electrode assembly and during delivery of the fluid.
 56. The method of claim 55 wherein the first member comprises a distal member and the second member comprises a proximal member. 